Leases - Lease expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Leases [Abstract]
Operating lease cost	$ 14.7		$ 41.0
Short-term lease cost	1.7		4.4
Amortization of right-of-use assets	0.9		3.8
Interest on lease liabilities	0.6		0.9
Total finance lease cost	1.5		4.7
Sublease income	0.2	$ 0.3	0.7	$ 0.7
Supplemental Cash Flow Information For Lessee
Operating cash flows from operating leases	12.7		40.2
Operating cash flows from finance leases	0.6		0.9
Financing cash flows from finance leases	1.2		3.3
Operating leases	3.8		14.0
Finance leases	$ 2.9		$ 18.0